1. Field of the Invention
The invention generally relates to an apparatus employed in the production of ribbon-shaped crystals and more particularly to an improved susceptor for facilitating induction heating of silicon melt.
2. Description of the Prior Art
The prior art is, of course, replete with devices adapted to be employed in the production of semi-conductor ribbon, such as silicon ribbon, suited for use in the production of solar cells.
For example, one known process for producing silicon ribbons employs a V-shaped longitudinal trough having an inner wall forming a die for confining silicon melt. The die is provided with a longitudinal slit at the lower end of the V-trough through which a slit of ribbon is pulled. This device comprises a shaping guide including a pair of plates arranged in a V-trough configuration and supported by a one-piece susceptor formed of graphite and heated by induction heating coils efficiently coupled with the susceptor to induce a heating of the susceptor.
While a small heating current incidentally may be established in the melt, by the R-F coil aforementioned, it has been found that the susceptor wall is maintained at a temperature greater than the temperature of the melt. For example, it has been determined that for a silicon melt having a melting point of 1420.degree. C., the average temperature of the susceptor wall is 50.degree. C. to 200.degree. C. hotter than the melt. This fact, it is believed, clearly supports the contention that the susceptor is heated by induced heating currents and that the melt is heated by the susceptor through conduction.
Such, of course, requires that the wall of the susceptor be heated to a temperature well above that at which the melt is required to be heated. As a consequence, excessive energy is consumed in the process.
It is, therefore, the general purpose of the instant invention to provide an improved apparatus which facilitates a direct coupling of an R-F coil with a silicon melt, whereby simplicity in construction, enhanced control of thermal gradients, and a conservation of input energy are realized.